This invention relates to automatic tire inflation systems for transportation vehicles, and specifically improvements in those that include an indicating device to signal when a tire is receiving air.
Automatic tire Inflation systems provide air to a vehicle""s tires even while the vehicle is in motion. In the event a tire has lost air pressure, the inflation system will send air to the leaking tire, usually from the frame of the vehicle through a rotary union aligned with the tire""s rotational axis. When the inflation system is delivering air, it is beneficial for the driver to be alerted that a tire is requiring inflation. The alert system can be a visual light, a screen display, an audio alarm, or another electronically activated device to warn the driver.
A common alert system uses a pressure regulator and a pressure switch. The pressure regulator is placed between a source of air pressure and the tires to limit the system""s inflation pressure and thereby prevent over inflation as shown in U.S. Pat. No. 3,276,503. A normally closed pressure switch is placed between the pressure regulator and the tires, and when a tire looses pressure, dynamic pressure losses cause the pressure downstream of the pressure regulator to drop and close the pressure switch. The signal ceases only when the pressure regulator delivers enough air to refill the tire and build enough pressure to open the pressure switch.
It is difficult for this method to be responsive because the pressure switch""s open and close pressure must be adjusted precisely below the regulator""s adjusted pressure. Temperature and friction change over time, and the dynamic components in both the pressure switch and pressure regulator do not always respond consistently. If the difference between the two adjusted settings is large, the signal will not be sent until a tire""s pressure has greatly decreased. If the difference between the adjusted settings is small, it is possible the switch will close and falsely send a signal due to normal fluctuations in the regulator""s output. Also, the presence of two adjustments leads to unnecessary complications in the field.
One design meant to overcome the insensitivity of the pressure regulator and pressure switch combination is the use of a flow switch, as in U.S. Pat. No. 5,767,398. Here the switch requires no adjustment and will close whenever the inflation system is sending air. One drawback to this system is that the operator will not be alerted if a tire has low air pressure and the system has no air pressure to deliver. If the automatic tire inflation system were turned off, the flow switch would not indicate low pressure in a tire to the driver since no air would flow through the switch. Another shortcoming is that a cluster of valves is difficult to package on a vehicle.
Proximity sensors have been used to remotely determine valves"" positions in many other applications. When a valve is used in processes where it is inaccessible, it can be desirable to know the valve""s position using a sensor. Usually these sensors are used on shut-off type valves with remote actuators so the valve""s position can be assured when remotely actuating the valves. The present invention is an improved sensor for detecting an air leak in a tire inflation system. Integrating a sensor directly into the tire inflation system""s pressure regulating valve offers advantages over existing methods.
Objects and Advantages
Tire inflation system designers have always included additional pressure switches or valves to determine the tires"" pressure status, apparently because the benefits of integrating a switch into a pressure regulator were not considered or understood. The object of the present invention is to provide such a system with an alert switch which will indicate a low tire pressure situation, even when the source of air pressure is depleted or turned off, and without requiring the separate adjustment of a switch, while meeting the needs of a present day commercial tire inflation system. By building the switch into the pressure regulator the switch will respond with certainty to the system""s operation. The only adjustment required is setting the pressure regulator. The need for additional valves or external switches is eliminated, helping to package the system within the vehicle. The switch will close immediately if a tire""s pressure falls, greatly improving sensitivity. In the event of a low tire pressure situation when there is no pressure from the source, the switch will also close to warn of the condition. In accordance with the present invention a pneumatic valve used in an automatic tire inflation system comprises an inlet, an outlet, and a spring biased pneumatically controlled actuator responsive to the outlet air pressure and capable of opening a normally closed valve seat to allow air flow from the inlet to the outlet to control outlet air pressure, while actuating a switch to indicate a warning signal.